Digitizing pen and tablet systems are used for a variety of electronic applications. These systems typically include a tablet, a position indicating pen, and associated electronics for determining the interaction between the writing surface and the position indicating pen. A digital data signal is typically derived to represent the relative position of the position indicating pen and the writing surface.
In prior art position indicating pens, an excitation circuit powers a signal transducer, producing a long-duration transmission signal waveform, or ringing, which then slowly decays. The wide transmission signal is then transmitted from the position indicating pen to external receivers. The wide transmission signal waveform is then analyzed, to determine the relative time for the signal to reach each receiver. The location of the pen is then determined, based on triangulation methods. Since the receiver is required to approximate where on each of the wide transmission signal waveforms to designate the estimated path length, the resulting determined pen location can be inaccurate.
Also, the resulting wide waveform requires that the period between subsequent output signals be extended, which results in less frequent updates for the current position of the pen. When a user directs a pen quickly across a writing area, such as a white board, the stroke of the pen is not accurately captured when the period between subsequent transmitter signals is large.
M. Phillips, T. Philbin, and B. Blesser, Coordinate Determining Device Using Spatial Filters, U.S. Pat. No. 4,963,703 (Oct. 16, 1990) disclose a digitizing tablet, in which "two sets of circuitous conductive lines form grids each connected at one end to a surrounding conductive loop. All outputs are measured from the conductive loop as a multiplexor sequentially grounds the grids one at a time. The outputs are fed through linear spatial filters which are used to produce intermediate signals which are in turn combined to arrive at raw position signals for a position indicating coil located over the work surface. Separate sets of linear spatial filters may be used to produce two raw position signals differently responsive to tilt which can then be combined to arrive at a true position insensitive to tilt". Phillips et al. also disclose a stylus having a single conductive coil, which is used as a position indicating implement over a work surface.
S. Payne, Ultrasonic Generator Drive Circuit, U.S. Pat. No. 3,975,650 (Aug. 17, 1976) discloses an ultrasonic generator, which "comprises a transducer which is adapted to vibrate in a fundamental frequency mode and the harmonic thereof in response to a square wave signal which is applied thereto. The transducer is a piezoelectric type which has a capacitor loading effect. A square wave generator is provided for generating a square voltage wave and driving means comprising high speed switching transistors is responsive to the signal from the square wave generator for driving the transducer with a square wave. The transistors are switchable between conducting and non-conducting states and are connected to the square wave generator so that the transistors are switched in phase opposition to each other. A non-resistant inductor connects the pair of transistors with the transducer to limit current flow and to permit application of the square wave to the transducer. An alternate embodiment utilizes a balancing transformer to eliminate the normal high common mode switching circuit".
T. Kuwabara, Booster Circuit, U.S. Pat. No. 3,824,447 (Jul. 16, 1974) discloses a booster circuit which "comprises a booster circuit capacitor and a plurality of capacitors, which are connected in parallel to a booster power supply for being charged when a voltage of a first level is applied to an input terminal of the booster circuit and, on the other hand, connected in series with each other when a voltage of a second level is applied thereto. The alternate application of the voltages having the first and second levels in repetitive manner allows the generation of a boosted voltage across the booster output capacitor.
J. Moriki, M. Shioji and T. Itoh, Drive Circuit for Piezoelectric High Voltage Generating Device, U.S. Pat. No. 4,054,806 (Oct. 18, 1977) disclose a high voltage generating device utilizing a piezoelectric transformer in which an inductance is connected between one of the drive electrodes of the piezoelectric transformer and an output terminal of a drive source, and a capacitor is connected across the two drive electrodes so that a variation of the output voltage of the device due to a change in the load is minimized. In addition, the effective range of the frequency characteristic of the output voltage is expanded and the temperature characteristic of the output voltage is improved.
D. Martinkovic, High Speed-High Voltage Switching for Low Power Consumption, U.S. Pat. No. 4,070,589 (Jan. 24, 1978) discloses a circuit in which "a capacitive load is charged through a series transistor. Peak charge currents for the load are drawn from a capacitive source whose charge is constantly maintained. Rapid discharge of the capacitive load is through a semiconductor diode and a cascade of transistors which act as switching elements".
L. Duren and A. Andersson, Ultrasonic Generators, U.S. Pat. No. 3,694,713 (Sep. 26, 1972) disclose "an ultrasonic generator including an amplifier coupled in oscillator configuration for initiating via an exciting impedance ultrasonic vibrations in an electro-acoustic element such as that associated with a dental implement. Connected in parallel with the exciting impedance is an additional impedance to form a tuned parallel resonance circuit. Maximum current is supplied to the exciting impedance through the amplifier and the primary winding of a current transformer also having a secondary winding connected in series with a capacitor to form a tuned series resonance circuit additionally emphasizing the maximum current".
I. Bourgeois, H. Daniels and R. Verlet, Arrangement for Generating Ultrasonic Oscillations, U.S. Pat. No. 3,819,961 (Jun. 25, 1974) disclose "a control circuit for a transducer comprising a tunable oscillator for driving the transducer at resonance, and a feedback loop responsive to the transducer comprising a phase detector which develops a series of pulse width modulated binary pulses, a D.C. source, an integrator, and various switching means to control the tunable oscillator".
I. Gilchrist, Circuit for Driving an Acoustic Transducer, U.S. Pat. No. 5,073,878 (Oct. 31, 1990) disclose a driver circuit for an acoustic transducer, which "includes a voltage regulator that provides a regulated DC output level for a high value load impedance and when the load impedance falls to a low value, its DC output exhibits a substantially reduced level. A transformer is connected between the voltage regulator and the acoustic transducer. A switching circuit is connected to the transformer and is responsive to a leading edge of a pulse input signal to reflect a low value impedance through the transformer to the voltage regulator. The switching circuit is further responsive to a lagging edge of a pulse input signal to reflect a high value impedance to the voltage regulator. A capacitive reactance circuit is coupled to the transformer and is responsive to the switching circuit reflecting a low value impedance to manifest a reduced charge state. When the switching circuit receives the lagging edge of the pulse input signal, the capacitive reactance circuit is recharged to the regulated DC output level, but over a charge time which prevents a step function signal from appearing across the transformer".
R. Hose, K. Riordan and S. Martin, Voltage Amplifier Circuit, U.S. Pat. No. 4,053,821 (Oct. 11, 1977) disclose a voltage multiplier circuit "which converts a relatively low voltage to a relatively high voltage with any undesirable voltage drops across any of the constituent components. A plurality of the disclosed voltage multiplier circuits may be cascaded together to increase the multiplied output voltage, wherein each multiplier stage of the cascaded circuits multiplies the input voltage by two".
K. Takehiko, Apparatus for Driving Piezoelectric Transformers, U.S. Pat. No. 3,708,701 (Jan. 2, 1973) discloses an apparatus for driving a transducer in which a resonance circuit is "comprised by an inductance and a capacitance connected in parallel and connected across the input electrodes of the transducer, and means for supplying a periodic pulse current of narrow width to the resonance circuit thereby driving the piezoelectric transducer by the energy delivered by the resonance circuit".
The disclosed prior art systems and methodologies thus provide circuits that can be used to power transducers, but fail to provide a circuit that powers a transducer with a short pulse input signal, which allows a the transducer to transmit a shortened output signal having distinct waveshape characteristics. The development of such a transducer input system would constitute a major technological advance.